System and method for adding a high voltage DC source to a power bus

ABSTRACT

A system for connecting first and second high voltage direct current (HVDC) sources in parallel to a bus includes one or more contactors connecting the first HVDC source to the bus. The system also includes a bus coupling circuit located between the second HVDC source and the bus that utilizes inductors to couple, in operation, couples the second HVDC source to the bus such that first and second HVDC sources are in parallel with the second positive output is connected to the positive rail and the second negative output connected to the negative rail. The inductors are first connected to the bus though auxiliary contactors and, after a predetermined time, main contactors are closed that provide a path around the inductors.

BACKGROUND

Exemplary embodiments pertain to the art of power distribution and, inparticular, to adding a high voltage DC source to an already powered DCbus.

Aircraft require electrical power to operate many parts of the aircraftsystem, including on-board flight control systems, lighting, airconditioning etc. The current and future generations of aircraft usemore and more electrical control in place of convention hydraulic,pneumatic etc. control. Such aircraft have advantages in terms of thesize and weight of the controls and power systems as well as in terms ofmaintenance and reliability.

Most current large commercial aircraft use electricity, on-board, in theform of an AC fixed frequency and/or variable frequency network. Stepshave been made to move from 115 V ac to 230 V ac and more recentdevelopments have allowed power supplies to supply high voltage dc(HVDC) e.g. +/−270 V dc, providing improvements in terms of additionalfunctionality, power supply simplification, weight savings and thus fuelefficiency.

Generally, voltage is provided on board aircraft in one of two (or more)ways. When the aircraft is on the ground, power comes from an externalground generator supplying, say 115 V ac at 400 Hz. An auto-transformerrectifier unit (ATRU) rectifies the supply voltage to provide voltagesrequired for the different loads on the aircraft. Instead of an ATRU,the power can be rectified by active rectification using power flowcontrollers.

When the aircraft is in the air the power comes from the aircraft engineor auxiliary power unit (APU) via a three-phase ac generator that isthen rectified. The rectified power is provided to a so-called DC bus.

BRIEF DESCRIPTION

Disclosed is a method of connecting first and second high voltage directcurrent (HVDC) sources in parallel to bus including a positive rail anda negative rail. The first HVDC source has a first positive output lineand a first negative output line and the second HVDC source having asecond positive output line and a second negative output line. Themethod includes: connecting the first HVDC source to the bus such thatthe first positive output line is connected to the positive rail and thefirst negative output line is connected to the negative rail; closing afirst auxiliary contactor to connect the second positive output line tothe positive rail through a first inductor; closing a second auxiliarycontactor to connect the second negative output line to the negativerail through a second inductor; closing, after a specified time, a firstmain contactor that is connected in parallel with the first auxiliarycontactor and the first inductor to connect the second positive outputline to positive rail and a second main contactor that is connected inparallel with the second auxiliary contactor and the second inductor toconnect the second negative output line to positive rail; and openingthe first and second auxiliary contactors.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the first HVDC sourcecan include a first generator connected to a first prime mover.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the second HVDC sourceincludes a second generator connected to a second prime mover.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the first prime movercan be one of: a low pressure spool of the gas turbine engine, a mediumpressure spool of the gas turbine engine or an auxiliary power unit.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the second prime moveris one of: a low pressure spool of a gas turbine engine, a mediumpressure spool of the gas turbine engine or an auxiliary power unit.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the second HVDC sourceincludes a second generator connected to a second prime mover, whereinthe second prime mover is a high pressure spool of the gas turbineengine.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the first HVDC sourceincludes a first generator connected to a first prime mover, wherein thefirst prime mover is a high pressure spool of the gas turbine engine.

Also disclosed is a system for connecting first and second high voltagedirect current (HVDC) sources in parallel to a bus including a positiverail and a negative rail, the first HVDC source having a first positiveoutput line and a first negative output line and the second HVDC sourcehaving a second positive output line and a second negative output line.The system includes one or more contactors connecting the first HVDCsource to the bus such that the first positive output line is connectedto the positive rail and the first negative output line is connected tothe negative rail. The system also includes a bus coupling circuitlocated between the second HVDC source and the bus that, in operation,couples the second HVDC source to the bus such that first and secondHVDC sources are in parallel, the second positive output is connected tothe positive rail and the second negative output is connected to thenegative rail. The bus coupling circuit includes: a positive linecoupler and a negative line coupler, the positive line coupler includinga first auxiliary contactor and a first inductor connected in series anda first main contactor connected in parallel with the series connectedfirst auxiliary contactor and first inductor, the negative line couplerincluding a second auxiliary contactor and a second inductor connectedin series and a second main contactor connected in parallel with theseries connected second auxiliary contactor and second inductor. Thesystem also includes a controller configured to: close the firstauxiliary contactor to connect the second positive output line to thepositive rail through the first inductor; close the second auxiliarycontactor to connect the second negative output line to the negativerail through the second conductor; and close the first and second maincontactors after a specified time has elapsed after the first or secondauxiliary contactors were closed.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the controller isfurther configured to open the first and second auxiliary contactorsafter the first and second main contactors are closed.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the first HVDC sourceincludes a first generator connected to a first prime mover.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the first prime moveris a high pressure spool of a gas turbine engine.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the second HVDC sourceincludes a second generator connected to a second prime mover, whereinthe second prime mover is one of: a low pressure spool of the gasturbine engine, a medium pressure spool of the gas turbine engine or anauxiliary power unit.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the second HVDC sourceincludes a battery.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the first prime moveris one of: a low pressure spool of a gas turbine engine, a mediumpressure spool of the gas turbine engine or an auxiliary power unit.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the second HVDC sourceincludes a second generator connected to a second prime mover, whereinthe second prime mover is a high pressure spool of the gas turbineengine.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the second HVDC sourceincludes a battery.

The system/method can also be used to offload power onto a source thatis not under aircraft control, such as ground power.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 is a schematic of a power bus that is initially driven by a firstpower source and to which a second power source is to be added inparallel; and

FIG. 2 is a flow chart illustrating a method of connecting two highvoltage DC sources to a bus in parallel according to one embodiment.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the Figures.

As discussed above, when the aircraft is in the air the power comes fromthe aircraft engine or auxiliary power unit (APU) generally providespower to the DC bus. In some instances it may be desirable to have twosources (e.g., generators) provide to the bus at the same time. Forexample, in the general case, a generator connects to the high pressurespool of a gas turbine engine via gear box. The power thus produced isconnected to the DC bus of the aircraft. In some instances it may bedesirable to add an additional source of DC power to the bus inparallel. For example, it may be desirable to add power from a secondgenerator connected to the low pressure spool or the APU or both to theDC bus. This can allow for the DC bus to provide more power for largerloads such as an electric propulsion system. Such instances can occuranytime increased electrical power to the DC bus is needed such asduring take-off.

Bringing two HVDC channels into parallel will produce a very largecurrent spike unless the voltages across capacitors connected to the DCbus are very close to one another. Another complication is that thereare two capacitor voltages to consider, one each for the upper and lowerrails of the DC bus. This current spike might weld a contactor formingthe connection closed or will at least shorten the useful life of thecontactor.

Disclosed is system where the current spike can be reduced or eliminatedwhen bringing two HVDC power channels into parallel.

In one prior approach to adding one HVDC source into parallel withanother is to temporarily lower the voltage of the channel requesting tocome on-line and use a pair of diodes and an auxiliary contactor to makethe parallel connection while the voltage of the channel coming on lineis ramped up. In this manner, the natural commutation of the diodesconnects the capacitors at the point(s) in time when their voltages areequal and thereby avoid a current spike. When current is detected inboth diodes, the main contactor is closed to provide paths around thediodes and the auxiliary contactors. While effective, that aboveapproach required sensors and had a complicated contactor switchingschemes described above. In addition, diodes have V_(f)*I_(f) conductionlosses.

Given these discoveries, herein disclosed is a system that utilizesseries connected inductors without requiring diodes (that is, in someembodiments, no diodes are included) to add an HDVC source. As idealinductors are energy storage elements which dissipate no real power.Power losses can be improved if inductor series resistance is minimized.Further, utilizing inductors as opposed to diodes can eliminate the needto lower the voltage of the HDVC channel being added. The disclosedsystem allows for busses with significantly different voltages duringcontactor closure to be paralleled without detrimental inrush current(due to the inherent property of inductors resisting instantaneouschanges in current) without complicated procedures where the channelvoltages are lowered.

FIG. 1 shows an example of bus 100 that includes a positive bus rail 102and negative bus rail 104. The terms positive and negative merely referto the fact that the rails 102, 104 can have a voltage differential. Forexample, the positive rail 102 can be at +270V and the negative rail 104can be a −270V. Of course, depending on how grounded, these voltagescould be +540V and 0V.

As illustrated the bus 100 is being driven by a first high voltagesource 110. The first high voltage source 110 includes a prime mover 112that drives a first AC generator 114. The prime mover 112 can be a spoolof the gas turbine engine. The prime mover 112 is a high pressure spoolof the gas turbine engine in one embodiment but can be other spools(e.g., low or medium) or can be an auxiliary power unit (APU) in oneembodiment. The prime mover 112 can be connected to the first ACgenerator 114 by a gear box as is known in the art. The output of thefirst AC generator 114 is provided to a first rectifier 116 thatconverts the AC power received form the first AC generator 114 into aHVDC power. As shown, the first rectifier 116 produces a positive output(V+) on a first positive output line 120 and a negative output (V−) on afirst negative output line 122. This can be accomplished in any knownmanner including having two rectifiers, one of which is inverting. Thefirst positive output line 120 and the first negative output line 122are connected to the positive and negative bus rails 102, 104,respectively.

First positive and negative smoothing capacitors 124, 126 are connectedbetween the first positive output line 120 and the first negative outputline 122, respectively, and ground to smooth the voltages provided onthe first positive output line 120 and the first negative output line122 (and thus, positive and negative bus rails 102, 104).

In shall be understood that the first high voltage source 110 can beconnected to the bus by one or more contactors 128, 129 on the firstpositive output line 120 and the first negative output line 122,respectively. In FIG. 1 the contactors 128, 129 are shown as beingclosed.

As discussed above, in some instances it may be desirable to add connecta second high voltage source 130 to the bus 100. Herein disclosed is abus coupling circuit 160 and method that may allow the second highvoltage source 130 to be added without creating a large current spike.

As shown, the second high voltage source 130 is not connected to the bus100 in FIG. 1 but based on the discussion herein, after the stepsdisclosed herein are performed, the second high voltage source 130 willbe connected to the bus 100 in parallel with the first high voltagesource 110. The first and second high voltage sources can also bereferred to as first and second high voltage direct current (HVDC)sources herein.

As illustrated, similar to the first high voltage source 110, the secondhigh voltage source 130 includes a second prime mover 142 that drives asecond AC generator 144. The second prime mover 142 can be another spoolof the gas turbine engine that is different than the first prime moveror can be an auxiliary power unit (APU). The second prime mover 142 canbe connected to the second AC generator 144 by a gear box as is known inthe art. The output of the second AC generator 144 is provided to asecond rectifier 146 that converts the AC signal received form thesecond AC generator 144 into a HVDC signal. As shown, the secondrectifier 146 produces a positive output (V+) on a second positiveoutput line 150 and a negative output (V−) on a second negative outputline 152. In another embodiment, the second high voltage source 130could be a battery. In such a case, elements 142, 144, and 146 could beomitted replaced with a battery shown schematically by block 300.

Second positive and negative smoothing capacitors 154, 156 are connectedbetween the second positive output line 150 and the second negativeoutput line 152, respectively, and ground to smooth the voltagesprovided on second positive output line 150 and the second negativeoutput line 152.

As illustrated, bus coupling circuit 160 is connected between the secondhigh voltage source 130 and the bus 100. After the steps herein areperformed, contactors 166 and 176 will couple the second positive outputline 150 and the second negative output line 152 to the positive andnegative bus rails 102, 104, respectively.

The bus coupling circuit 160 includes positive line coupler 161 and anegative line coupler 171 that, respectively, are connected to thesecond positive output line 150 and the second negative output line 152and the positive and negative bus rails 102, 104.

Both the positive line coupler 161 and the negative line coupler 171include main contactors that are connected in parallel to a seriallyconnected inductor/auxiliary contactor combination. In particular, thepositive line coupler 161 includes a first auxiliary contactor 162serially connected to a first inductor 164 such that the inductor 164allows current flow from the second high voltage source 130 to the bus100. The order of the two components can be reversed. A first maincontactor 166 is connected in parallel with the first auxiliarycontactor 162/first inductor 164 combination.

In addition, negative positive line coupler 141 includes a firstauxiliary contactor 162 serially connected to a second inductor 174 suchthat the inductor 164 allows current flow from the bus 100 to return tothe second high voltage source 130. The order of the two components canbe reversed. A second main contactor 176 is connected in parallel withthe second auxiliary contactor 172/second inductor 174 combination.

Operation of the second high voltage source 130 and the bus couplingcircuit 160 will now be described in the context of adding the secondhigh voltage source 130 in parallel to the first high voltage source 110at a time that the first high voltage source 110 is driving the bus 100.The discussion will refer to both FIGS. 1 and 2.

As indicated at block 202, the first and second auxiliary contactors162, 172 are closed. Then, after a predetermined or specified time(waiting time) after the first and second auxiliary contactors wereclosed, the main contactors the main contactors 166 and 176 are closedand the auxiliary contactors 162, 172 can be opened as indicated atblock 204. The waiting time is indicated in FIG. 2 by block 203 and maybe pre-determined using worst case system or component tolerances, orset based on current or other sensed parameters if available.

Based on the above description, the skilled artisan will realize thatthe natural resistance to instantaneous current changes in the first andsecond inductors 164, 174 is used to connect the capacitors of each highvoltage source 110, 130 at the point(s) in time when their voltage isroughly equal and thereby avoid a current spike. In one embodiment, themain contactors 166 and 176 can each have two poles and be actuated by asingle solenoid.

Further, it should be noted that as opposed to other approaches thatinvolve either or both an inductor/diode, therein, when the maincontactors 166/176 are closed and the auxiliary contactors 162, 172 canbe opened any element that can impede or otherwise slow powerdistribution (e.g., an inductor or diode) is effectively removed fromthe circuit.

The term “about” is intended to include the degree of error associatedwith measurement of the particular quantity based upon the equipmentavailable at the time of filing the application.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof.

While the present disclosure has been described with reference to anexemplary embodiment or embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe present disclosure. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this present disclosure, but that the present disclosurewill include all embodiments falling within the scope of the claims.

What is claimed is:
 1. A method of connecting first and second highvoltage direct current (HVDC) sources in parallel to bus including apositive rail and a negative rail, the first HVDC source having a firstpositive output line and a first negative output line and the secondHVDC source having a second positive output line and a second negativeoutput line, the method including: connecting the first HVDC source tothe bus such that the first positive output line is connected to thepositive rail and the first negative output line is connected to thenegative rail; closing a first auxiliary contactor to connect the secondpositive output line to the positive rail through a first inductor;closing a second auxiliary contactor to connect the second negativeoutput line to the negative rail through a second inductor; closing,after a specified time, a first main contactor that is connected inparallel with the first auxiliary contactor and the first inductor toconnect the second positive output line to positive rail and a secondmain contactor that is connected in parallel with the second auxiliarycontactor and the second inductor to connect the second negative outputline to positive rail; and opening the first and second auxiliarycontactors.
 2. The method of claim 1, wherein the first HVDC sourceincludes a first generator connected to a first prime mover.
 3. Themethod of claim 2, wherein the first prime mover is a high pressurespool of a gas turbine engine.
 4. The method of claim 3, wherein thesecond HVDC source includes a second generator connected to a secondprime mover, wherein the second prime mover is one of: a low pressurespool of the gas turbine engine, a medium pressure spool of the gasturbine engine or an auxiliary power unit.
 5. The method of claim 2,wherein the first prime mover is one of: a low pressure spool of a gasturbine engine, a medium pressure spool of the gas turbine engine or anauxiliary power unit.
 6. The method of claim 3, wherein the second HVDCsource includes a second generator connected to a second prime mover,wherein the second prime mover is a high pressure spool of the gasturbine engine.
 7. A system for connecting first and second high voltagedirect current (HVDC) sources in parallel to a bus including a positiverail and a negative rail, the first HVDC source having a first positiveoutput line and a first negative output line and the second HVDC sourcehaving a second positive output line and a second negative output line,the system including: one or more contactors connecting the first HVDCsource to the bus such that the first positive output line is connectedto the positive rail and the first negative output line is connected tothe negative rail; a bus coupling circuit located between the secondHVDC source and the bus that, in operation, couples the second HVDCsource to the bus such that first and second HVDC sources are inparallel, the second positive output is connected to the positive railand the second negative output is connected to the negative rail, thebus coupling circuit including: a positive line coupler and a negativeline coupler, the positive line coupler including a first auxiliarycontactor and a first inductor connected in series and a first maincontactor connected in parallel with the series connected firstauxiliary contactor and first inductor, the negative line couplerincluding a second auxiliary contactor and a second inductor connectedin series and a second main contactor connected in parallel with theseries connected second auxiliary contactor and second inductor; and acontroller configured to: close the first auxiliary contactor to connectthe second positive output line to the positive rail through the firstinductor; close the second auxiliary contactor to connect the secondnegative output line to the negative rail through the second conductor;and close the first and second main contactors after a specified timehas elapsed after the first or second auxiliary contactors were closed.8. The system of claim 7, wherein the controller is further configuredto open the first and second auxiliary contactors after the first andsecond main contactors are closed.
 9. The system of claim 7, wherein thefirst HVDC source includes a first generator connected to a first primemover.
 10. The system of claim 9, wherein the first prime mover is ahigh pressure spool of a gas turbine engine.
 11. The system of claim 9,wherein the second HVDC source includes a second generator connected toa second prime mover, wherein the second prime mover is one of: a lowpressure spool of the gas turbine engine, a medium pressure spool of thegas turbine engine or an auxiliary power unit.
 12. The system of claim11, wherein the second HVDC source includes a battery.
 13. The system ofclaim 9, wherein the first prime mover is one of: a low pressure spoolof a gas turbine engine, a medium pressure spool of the gas turbineengine or an auxiliary power unit.
 14. The system of claim 13, whereinthe second HVDC source includes a second generator connected to a secondprime mover, wherein the second prime mover is a high pressure spool ofthe gas turbine engine.
 15. The system of claim 13, wherein the secondHVDC source includes a battery.